This can absolutely be true for many systems and optimisations, but Fuller's premise is that new technology will allow efficiency improvements or substitutions

This can absolutely be true for many systems and optimisations, but Fuller's premise is that new technology will allow efficiency improvements or substitutions that would not be possible in an extant system. For example one might come up with many ways to optimise the use of meeting rooms in an office, maybe making the rooms smaller to allow more simultaneous meetings, but now they're too cramped and you can't get as many people in a meeting. Maybe you add screens and network connections for presentations, but that's expensive, Tradeoffs, tradeoffs. However if you switch to a new technology like desktop videoconferencing you can get rid of the meeting rooms completely. Or you can reduce the number of meeting rooms by 5x and make the remaining ones bigger and higher tech for much better in person meetings that remain, at much lower total cost. New technology can completely eliminate or restructure whole categories of optimisation tradeoff.